Police and ambulances arrive at the scene of a school shooting at Sandy Hook Elementary School in Newtown, Conn., on Friday. / Don Emmert, AFP/Getty Images

by Gary Stoller, USA TODAY

by Gary Stoller, USA TODAY

A Newtown school staffer tells in her first interview what she lived through at Sandy Hook Elementary School.

Shari Thornberg says she was running late and fears she passed the gunman when she walked through the parking lot to the front doors of Sandy Hook Elementary School at 9:30 Friday morning.

That was the time, police say, that 20-year-old Adam Lanza entered the school for an attack that killed 20 children and six adults, and wounded two others. Police say he earlier shot his mother to death in their home.

Thornberg, an educational assistant for a fourth-grader with special needs, says the school's doors were locked and she was buzzed in. She held the door open for a co-worker and walked through the foyer into the principal's office, where she signed in and glanced at the staff news bulletin.

Principal Dawn Hochsprung, who would be killed moments later, was not in the office. A school nurse and an office worker were there.

Thornberg left the office, turned left into the foyer and left again down a hallway past the cafeteria. She went into a math-science room to hang her coat and store her lunch.

She happily showed two colleagues a photo of her 17-year-old son, Patrick, a Newtown High School senior and football player.

"Then we heard pop-pop-pop, pop-pop-pop, and I thought, 'That's a weird noise,'" Thornberg says. "I first thought it was the janitor taking down risers and setting up tables."

The school's intercom was on, and Thornberg next heard "more shots, screaming, crying and whimpering." She heard the janitor yell at the gunman, "'Put the gun down! Put the gun down.'"

She and two colleagues locked the door of the teacher's room, "and the three of us struggled to get in a small closet.

"We heard everything over the intercom, though it was muffled because our closet door was closed," she says. "We just waited in the closet, saying The Lord's Prayer out loud over and over again, and praying for all staff members and the children."

Thornberg says they waited in the closet for "what seemed like forever." Police said the gunman entered at 9:30 a.m. and the shooting was over in about 10 minutes.

"It was scary when we heard the classroom door jiggle and thought it was the gunman," Thornberg says. "When the shooting was over, we learned it was the janitor checking to see whether the door was locked."

Thornberg says she was told by school staff that the gunman entered the principal's office and left after seeing no one there. The nurse and the office worker were hiding under desks, and the nurse could see the gunman's pants leg, Thornberg says.

The gunman went down the left hallway. Hochsprung and school psychologist Mary Sherlach were killed, and a teacher whom police have not yet identified was wounded, when they went into the hallway from a conference room, Thornberg says.

The injured teacher crawled back into the room where at least three other adults were inside, and they locked the door.

A substitute kindergarten teacher, whom police also have not identified, was slightly wounded further down the hallway.

The gunman, Thornberg says, did not enter the first classroom on the left where the teacher, Kaitlin Roig, had piled 16 first-graders on top of one another in the bathroom.

"I think Dawn coming out of the conference room may have distracted the gunman from going into that classroom, Thornberg says.

The gunman then moved down the hallway to two other first-grade classrooms and fired into both rooms, she says. When he was finished, he fatally shot himself, police say.

Thornberg says police arrived at the school and, unaware of who was doing the shooting, apprehended the janitor and another man outside the school.

Most of the children and Thornberg raced to a firehouse down the street, where "it was chaos," she says.

"Who would have thought this would happen in an idyllic little school in the woods where you would want your kids to go to?" Thornberg asks.

She says the school's teachers are traumatized, including some who are not ready to return to work and some who are questioning whether to resume their teaching careers.

"My biggest concern is how we are going to move forward," Thornberg says.

But then, thinking of younger generations and her three children - 17-year-old Patrick, 20-year-old Eric and 22-year-old Colleen, who all went through the Newtown school system - Thornberg says she is determined to take on the future.

"Our children have lived through the Sept. 11 attack, the Aurora, Colo., movie massacre and now this attack, and you realize how much evil is in the world," she says. "I feel for their generation and know they need much more love and concern. Our children need us to be strong."